Fix 'Please select at least one DLL implementing the IEdmAddIn5 interface' error

Symptoms

The following error is shown when adding the add-in with SOLIDWORKS PDM administration tool: Please select at least one DLL implementing the IEdmAddIn5 interface

Cause

Error happens when SOLIDWORKS PDM cannot find the class which implements the IEdmAddIn5 which corresponds to the add-in.

In order for the add-in class to be visible to SOLIDWORKS PDM, it must be public and com visible.

Examples of incorrect declaration of add-in

Class is not marked as COM Visible

public class PdmAddIn : IEdmAddIn5
{
}

Class doesn't have access modifiers (private by default)

[ComVisible(true)]
class PdmAddIn : IEdmAddIn5
{
}

Class marked as internal

[ComVisible(true)]
internal class PdmAddIn : IEdmAddIn5
{
}

Resolution

Make sure that add-in class is public and decorated with ComVisible attribute with value set to True

[ComVisible(true)]
public class PdmAddIn : IEdmAddIn5
{
}